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Abstract:

A photoluminescent daylight panel for converting higher energy shorter
wavelength daylight to lower energy longer wavelength light comprises: a
light transmissive substrate; at least one photoluminescent material
configured to absorb at least a portion of daylight radiation of
wavelengths between about 350 nm and about 450 nm and convert it to light
with a wavelength greater than about 600 nm.

Claims:

1. A photoluminescent daylight panel for converting higher energy shorter
wavelength daylight to lower energy longer wavelength light, the panel
comprising: a light transmissive substrate; at least one photoluminescent
material configured to absorb at least a portion of daylight radiation of
wavelengths between about 350 nm and about 450 nm and convert it to light
with a wavelength greater than about 600 nm.

2. The panel of claim 1, wherein the at least one photoluminescent
material comprises one or more phosphors.

3. The panel of claim 1, wherein the at least one photoluminescent
material comprises quantum dots.

4. The panel of claim 1, wherein the at least one photoluminescent
material comprises an orange silicate-based phosphor of general
composition A3Si(O,D)5 in which A is at least one of Sr, Ba, Mg
and Ca and D is a at least one of Cl, F, N and S.

5. The panel of claim 4, wherein the silicate-based orange phosphor has
the formula (Sr1-xMx)yEuzSi0.sub.5, in which M is at
least one of a divalent metal Ba, Mg, Ca and Zn; 0<x≦0.5;
2.6.ltoreq.y≦3.3; 0.001.ltoreq.z≦0.5 and subject to the
proviso that y is not 3 when M is Ba.

6. The panel of claim 1, wherein the at least one photoluminescent
material comprises an aluminum-silicate-based orange phosphor of general
composition
(Sr1-x-yMxTy)3-mEum(Si1-zAlz)O5,
in which M is at least one of a divalent metal Ba, Mg, and Ca; T is a
trivalent metal Y, La, Ce, Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb,
Lu, Th, Pa and U; 0.ltoreq.x≦0.4; 0.ltoreq.y≦0.4;
0.ltoreq.z≦0.2; and 0.001.ltoreq.m≦0.5.

7. The panel of claim 6, wherein the aluminum-silicate-based orange
phosphor further comprises a halogen F, Cl or Br.

8. The panel of claim 7, wherein the halogen resides on oxygen lattice
sites within the silicate crystal.

9. The panel of claim 1, wherein the at least one photoluminescent
material is a silicate-based yellow phosphor of general composition
A2Si(O,D)4 in which A comprises at least one Sr, Ca, Ba, Mg, Zn
and Cd and D is a is at least one F, Cl, Br, I, P, S and N.

10. The panel of claim 9, wherein the dopant D is present in the phosphor
in an amount ranging from about 0.01 to 20 mole percent.

11. The panel of claim 10, wherein at least some of the dopant
substitutes for oxygen anions to become incorporated into the crystal
lattice of the phosphor.

12. The panel of claim 9, wherein the silicate-based yellow phosphor has
the formula (Sr1-x-BaxMy)2Si(O,D)4:Eu2+ in
which 0.ltoreq.x≦1 and where 0.ltoreq.y≦1 when M is Ca;
0.ltoreq.y≦1 when M is Mg; and 0.ltoreq.y≦1 when M is Zn
and Cd.

14. The panel of claim 1, wherein the at least one photoluminescent
material is incorporated within the light transmissive substrate.

15. The panel of claim 1, wherein the at least one photoluminescent
material is distributed in a wavelength conversion layer on the light
transmissive substrate.

16. The panel of claim 15, and further comprising a light diffusing layer
on a surface of the layer of at least one photoluminescent material.

17. The panel of claim 15, and further comprising a further light
transmissive substrate, the wavelength conversion layer being located
between the light transmissive substrate and the further light
transmissive substrate.

19. A light tube for providing daylight to an interior of a structure,
comprising: a first light transmissive surface exposed to the daylight; a
second light transmissive surface exposed to the interior of the
structure; and a light reflective tubular chamber for guiding light
between the first surface and the second surface; and at least one
photoluminescent material for converting higher energy shorter wavelength
daylight to lower energy longer wavelength light, the at least one
photoluminescent material configured to absorb at least a portion of
daylight radiation of wavelengths between about 350 nm and about 450 nm
and convert it to light with a wavelength greater than about 600 nm.

20. The light tube of claim 19, wherein the first surface includes the at
least one photoluminescent material.

21. The light tube of claim 19, wherein the second surface includes the
photoluminescent material.

22. The light tube of claim 19, wherein the photoluminescent material is
distributed in a light transmissive substrate located between the first
and second surfaces.

23. The light tube of claim 19, wherein the photoluminescent material is
distributed in a wavelength conversion layer, the wavelength conversion
layer and a light transmissive substrate forming a panel that is situated
between the first and second surfaces.

24. The light tube of claim 23, wherein the panel covers at least a part
of an inner surface of the light tube.

25. The light tube of claim 19, wherein the at least one photoluminescent
material comprises an orange silicate-based phosphor of general
composition A3Si(O,D)5 in which A is at least one of Sr, Ba, Mg
and Ca and D is a at least one of Cl, F, N and S.

26. The light tube of claim 25, wherein the silicate-based orange
phosphor has the formula (Sr1-xMx)yEuzSi0.sub.5, in
which M is at least one of a divalent metal Ba, Mg, Ca and Zn;
0<x≦0.5; 2.6.ltoreq.y≦3.3; 0.001.ltoreq.z≦0.5 and
subject to the proviso that y is not 3 when M is Ba.

28. The light tube of claim 27, wherein the aluminum-silicate-based
orange phosphor further comprises a halogen F, Cl or Br.

29. The light tube of claim 28, wherein the halogen resides on oxygen
lattice sites within the silicate crystal.

30. The light tube of claim 19, wherein the at least one photoluminescent
material is a silicate-based yellow phosphor of general composition
A2Si(O,D)4 in which A comprises at least one Sr, Ca, Ba, Mg, Zn
and Cd and D is a is at least one F, Cl, Br, I, P, S and N.

31. The light tube of claim 30, wherein the dopant D is present in the
phosphor in an amount ranging from about 0.01 to 20 mole percent.

32. The light tube of claim 31, wherein at least some of the dopant
substitutes for oxygen anions to become incorporated into the crystal
lattice of the phosphor.

33. The light tube of claim 31, wherein the silicate-based yellow
phosphor has the formula
(Sr1-x-BaxMy)2Si(O,D)4:Eu2+ in which
0.ltoreq.x≦1 and where 0.ltoreq.y≦1 when M is Ca;
0.ltoreq.y≦1 when M is Mg; and 0.ltoreq.y≦1 when M is Zn
and Cd.

Description:

[0001] This present application claims the benefit of priority to U.S.
Provisional Application Ser. No. 61/718,688, filed Oct. 25, 2012, which
is hereby incorporated by reference in its entirety.

FIELD

[0002] This disclosure relates to daylight panels, and in particular to
daylight panels that convert the color temperature of daylight (sunlight)
using one or more photoluminescent materials. More especially, although
not exclusively, embodiments concern daylight panels that convert
daylight into a warm white light product.

BACKGROUND

[0003] Although daylight (sunlight) passing through windows, skylights,
and light tubes (also referred to as light pipes) can be used as a free
source of high quality illumination, it typically has a correlated color
temperature (CCT) between 5000-6500K, which is classified as "cool white"
and may not be preferred for interior environments. As a result, offices
and homes often use conventional artificial lighting during the day to
generate a more desirable "warm white" light even though sufficient
daylight is available. Offices and commercial properties typically use
"warm white" light with a CCT between 3500-4000K and homes typically use
a "warmer white" light with a CCT of 2700K.

[0004] When windows, skylights, and light tubes are used in commercial
office spaces in combination with fluorescent lighting fixtures
(typically fluorescent tube troffers), they tend to stand out due to
their "cool white" color as compared with adjacent fluorescent fixtures.
Although filtering could be used to adjust the CCT of daylight from a
"cool white" color to a "warm white" color, filters employ a subtractive
process and can reduce the amount of useable light by as much as 50% or
more. Therefore, there is a need for a daylight panel that at least in
part addresses these problems.

SUMMARY

[0005] Embodiments of the invention concern daylight panels that are
capable of converting the color temperature of daylight using a
photoluminescent material. In some embodiments, the daylight panel
comprises a light transmissive substrate that includes a photoluminescent
material, such as a phosphor or quantum dot material. The
photoluminescent material converts a portion of the daylight, typically
in the UV to blue part of the spectrum, to the orange and red part of the
spectrum which combined with the remaining unconverted daylight generate
a modified daylight emission product with a lower CCT.

[0006] According to one embodiment a photoluminescent daylight panel for
converting higher energy shorter wavelength daylight to lower energy
longer wavelength light, comprises: a light transmissive substrate; at
least one photoluminescent material configured to absorb at least a
portion of daylight radiation of wavelengths between about 350 nm and
about 450 nm and convert it to light with a wavelength greater than about
600 nm.

[0007] The at least one photoluminescent material can comprise one or more
phosphors. Alternatively and/or in addition the at least one
photoluminescent material comprises quantum dots.

[0008] Where the at least one photoluminescent material comprises a
phosphor the phosphor preferably comprises a yellow or orange
silicate-based phosphor and/or an orange aluminum-silicate-based
phosphor. Preferably the orange silicate-based phosphor has a general
composition A3Si(O,D)5 in which A is at least one of Sr, Ba, Mg
and Ca and D is a at least one of Cl, F, N and S. More particularly, the
silicate-based orange phosphor has the formula
(Sr1-xMx)yEuzSi05, in which M is at least one of
a divalent metal Ba, Mg, Ca and Zn; 0<x≦0.5;
2.6≦y≦3.3; 0.001≦z≦0.5 and subject to the
proviso that y is not 3 when M is Ba.

[0009] The aluminum-silicate-based orange phosphor preferably has a
general composition
(Sr1-x-yMxTy)3-mEum(Si1-zAlz)O5,
in which M is at least one of a divalent metal Ba, Mg, and Ca; T is a
trivalent metal Y, La, Ce, Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb,
Lu, Th, Pa and U; 0≦x≦0.4; 0≦y≦0.4;
0≦z≦0.2; and 0.001≦m≦0.5. Such a phosphor can
further comprise a halogen F, Cl or Br. It is believed that the halogen
resides on oxygen lattice sites within the silicate crystal.

[0010] The silicate-based yellow phosphor preferably has a general
composition A2Si(O,D)4 in which A comprises at least one Sr,
Ca, Ba, Mg, Zn and Cd and D is a is at least one F, Cl, Br, I, P, S and
N. In such phosphors the dopant D is present in an amount ranging from
about 0.01 to 20 mole percent. It is believed that at least some of the
dopant substitutes for oxygen anions to become incorporated into the
crystal lattice of the phosphor. More particularly the silicate-based
yellow phosphor has the formula
(Sr1-x-BaxMy)2Si(O,D)4:Eu2+ in which
0≦x≦1 and where 0≦y≦1 when M is Ca;
0≦y≦1 when M is Mg; and 0≦y≦1 when M is Zn
and Cd.

[0011] In preferred embodiment the at least one photoluminescent material
is a phosphor selected from the group consisting of:

[0020] In some embodiments the at least one photoluminescent material is
incorporated within the light transmissive substrate. Alternatively, the
at least one photoluminescent material can be distributed in a wavelength
conversion layer on the light transmissive substrate.

[0021] Particularly where the photoluminescent material comprises one or
more phosphors and to improve the visual appearance of the panel, the
panel can further comprise a light diffusing layer on a surface of the
layer of at least one photoluminescent material.

[0022] The panel can further comprise a second light transmissive
substrate, the wavelength conversion layer being located between the
light transmissive substrate and the second light transmissive substrate.

[0023] The light transmissive substrate can be substantially planar or
alternatively arcuate in form and be convex or concave.

[0024] According to a further aspect of some embodiments of the invention,
a light tube for providing daylight to an interior of a structure
comprises: a first light transmissive surface exposed to the daylight; a
second light transmissive surface exposed to the interior of the
structure; and a light reflective tubular chamber for guiding light
between the first surface and the second surface; and at least one
photoluminescent material for converting higher energy shorter wavelength
daylight to lower energy longer wavelength light, the at least one
photoluminescent material configured to absorb at least a portion of
daylight radiation of wavelengths between about 350 nm and about 450 nm
and convert it to light with a wavelength greater than about 600 nm.

[0025] The at least one photoluminescent material can be included in the
first and/or second surfaces and/or distributed in a light transmissive
substrate located between the first and second surfaces.

[0026] The photoluminescent material can be distributed in a wavelength
conversion layer, the wavelength conversion layer and a light
transmissive substrate forming a panel that is situated between the first
and second surfaces.

[0027] The panel can cover at least a part of an inner surface of the
light tube.

[0028] Further details of aspects, objects, and advantages of the
invention are described below in the detailed description, drawings and
claims. Both the foregoing general description and the following detailed
description are exemplary and explanatory, and are not intended to be
limiting as to the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order that the present invention is better understood, daylight
panels, light tubes, a skylight and a window in accordance with
embodiments of the invention will now be described, by way of example
only, with reference to the accompanying drawings in which like reference
numerals are used to denote like parts, and in which:

[0030] FIG. 1 illustrates the power density spectrum for daylight and
photopic response of the human eye;

[0031]FIG. 2 is a schematic diagram of a daylight panel in accordance
with an embodiment of the invention;

[0036] FIGS. 7A-7C are schematic diagrams of daylight panels in accordance
with embodiments of the invention;

[0037] FIGS. 8A and 8B are schematic diagrams of daylight panels in
accordance with embodiments of the invention;

[0038] FIGS. 9A-9C are schematic diagrams illustrating light tubes in
accordance with embodiments of the invention;

[0039] FIG. 10 is a schematic diagram of a skylight in accordance with an
embodiment of the invention; and

[0040] FIG. 11 is a schematic diagram of a window in accordance with an
embodiment of the invention.

DETAILED DESCRIPTION

[0041] Various embodiments are described hereinafter with reference to the
figures. It should be noted that the figures are not necessarily drawn to
scale. It should also be noted that the figures are only intended to
facilitate the description of the embodiments, and are not intended as an
exhaustive description of the invention or as a limitation on the scope
of the invention. In addition, an illustrated embodiment need not have
all the aspects or advantages shown. An aspect or an advantage described
in conjunction with a particular embodiment is not necessarily limited to
that embodiment and can be practiced in any other embodiments even if not
so illustrated. Also, reference throughout this specification to "some
embodiments" or "other embodiments" means that a particular feature,
structure, material, or characteristic described in connection with the
embodiments is included in at least one embodiment. Thus, the appearances
of the phrase "in some embodiment" or "in other embodiments" in various
places throughout this specification are not necessarily referring to the
same embodiment or embodiments.

[0042] For the purposes of illustration only, the following description is
made with reference to photoluminescent material embodied as phosphor
materials. However, the invention is applicable to any type of
photoluminescent material, such as for example quantum dots. A quantum
dot is a portion of matter (e.g., semiconductor) whose excitons are
confined in all three spatial dimensions that may be excited by excited
by radiation energy to emit light of a particular wavelength or range of
wavelengths. As such, the invention is not limited to phosphor material
based daylight panels unless claimed as such.

Principle of Operation

[0043] As discussed earlier, many working environments utilize daylight
(sunlight) that passes through windows, skylights, and light tubes as a
free source of high quality illumination. However, daylight has a typical
Correlated Color Temperature (CCT) between ≈5000K and
≈6500K, which is classified as "cool white" and may not be
preferred for interior environments. As a result, offices, factories,
homes and other environments capable of being lit by daylight, frequently
use conventional artificial lighting (e.g., fluorescent lighting) during
the day to generate a more desirable "warm white" light. Offices and
commercial properties typically use "warm white" light with a CCT between
about 3500K and about 4000K and homes typically use "warmer white" light
with a CCT of about 2700K.

[0044] When windows, skylights, and light tubes are used in office spaces
in combination with fluorescent lighting fixtures, they can stand out due
to their cooler white appearance (i.e. higher CCT). Whilst filtering can
be used to adjust the CCT of daylight from a "cool white" color to a
"warm white" color, filtering is a subtractive process that may reduce
the amount of useable light by as much as 50% or more.

[0045] FIG. 1 is an example of the daylight color spectrum showing power
density (Wm-2 nm-1) versus wavelength (nm) for daylight
(sunlight). The photopic response of the human eye (human eye
sensitivity) is also shown in FIG. 1. As can be seen in the figure, the
daylight spectrum includes a high power density (portion) of blue to
violet light (e.g., wavelengths shorter than about 500 nm) and a
relatively lower power density of orange to red light (e.g., wavelengths
longer than about 600 nm). Because of the relatively higher power density
of blue to violet light and the relatively lower power density of orange
to red light, daylight exhibits a CCT of "cool white". To transform
daylight to exhibit a CCT of "warm white" or "warmer white", the spectral
content needs to be converted such that it includes a higher power
density of orange to red light and a lower power density of blue to
violet light.

[0046] The human eye is sensitive to at least three "colors" of light: red
(R), green (G) and blue (B). As described above cool white light, such as
daylight, has an abundance of blue light (light with a wavelength shorter
than about 500 nm), plenty of green light, but relatively lower amounts
of orange/red (light of wavelength longer than about 600 nm). The present
invention resides in some respects to selectively converting at least a
portion of the violet to blue light (e.g. light with wavelengths shorter
than about 500 nm) into orange/red light (e.g. light with wavelengths
longer than about 600 nm) to modify (convert) the daylight color to a
balanced warm white. It is to be noted that the amount of green light
should be balanced with the new amounts of blue and orange/red light, but
may not need to be significantly shifted like the blue. A further benefit
with daylight is the large amount of violet, near UV and UV light (350 nm
to 430 nm) that is in the spectrum. These high energy photons generate
far fewer lumens of light or no lumens at all since the human eye rapidly
loses the ability to see short wavelength light of less than about 450 nm
(see FIG. 1--Photopic response). Lumens are a measurement of the human's
eye sensitivity to a specific color. Blue, violet and UV light have
higher energy per photon but low lumens because the eye is not sensitive
to these shorter wavelengths. By converting this shorter wavelength, low
visibility, low lumen light into higher visibility longer wavelength
orange/red, generates more lumens without sacrificing the more visible
parts of the blue spectrum.

[0047] Daylight panels in accordance with embodiments of the invention
utilize photoluminescent materials to convert blue and shorter wavelength
light such as violet, near UV and UV regions of the daylight spectrum to
light in the orange to red part of the spectrum thereby modifying the
color temperature from a cool white to warm white. Phosphor materials
used in fluorescent lighting are generally unsuitable for this
application because they are designed for mercury generated UV light. As
shown in FIG. 1 there is a relatively low amount of UV light in the
daylight spectrum and such phosphor materials are consequently
unsuitable. The inventors have discovered that the most efficient part of
the spectrum for conversion is in the region 350 nm to 450 nm where there
is available energy in daylight and the human eye sensitivity is low or
nonexistent. An example of preferred phosphor materials that are
efficient at conversion excitation radiation wavelengths of 350 nm to 450
nm are yellow and orange silicates-based phosphors and orange
aluminum-silicate-based phosphors as described below. Such phosphors down
convert (down converts in terms of energy) a broad range of shorter
wavelength light into longer wavelength yellow or orange light spanning a
range of wavelengths of about 500 nm to about 650 nm. Typically such
orange phosphors have a peak emission wavelength of 570 nm to 590 nm.
Although shorter wavelength light can be converted to red light this may
be undesirable as the resulting converted daylight will not fall onto the
black body curve and can result in a pink/violet cast to the daylight
panel. As a result it is preferred, though not limited, to use yellow to
orange photoluminescent materials.

Description of Exemplary Embodiments

[0048]FIG. 2 is a schematic diagram of a daylight panel 100 in accordance
with an embodiment of the invention. Daylight (Sunlight) 110 is
represented by the symbols λ1, λ2, λ3
where each symbol represents a different range of wavelengths that
collectively make up the daylight spectrum. The symbol λ1
represents the portion of the daylight having wavelengths below about 450
nm (i.e. typically 350 nm to 450 nm), the symbol λ2 represents
the portion of the daylight having wavelengths between about 450 nm and
600 nm and the symbol λ3 represents the portion of daylight
having wavelengths above about 600 nm (i.e. 600 nm to 750 nm). The
daylight panel 100 is operable to absorb at least a proportion of the
portion λ1 of the daylight with wavelengths below about 450 nm
and convert this into light having a wavelength λ4 longer than
about 600 nm. The daylight panel 100 also transmits the portions of the
daylight λ2 and λ3 together with unconverted light
of wavelengths λ1. In this way, the modified daylight emission
product 120 of the daylight panel 100 comprises a color spectrum that is
a mixture of the wavelength distributions λ1, λ2,
λ3 and λ4. As a result of the conversion, the
emission product 120 now includes a higher power density of orange to red
light and a reduced power density of blue to violet light, which results
in a "warm white" or "warmer white" CCT that may be more preferable for
use in offices and homes.

[0050] The light transmissive substrate 130 can be any material that is
substantially transmissive to light in a wavelength range from about 300
nm (ultra violet) to 740 nm (near infra red) and can include a light
transmissive polymer such as a polycarbonate or acrylic or a glass such
as a borosilicate glass, or any other suitable light transmissive
material. In some embodiments, the light transmissive substrate 130 can
be a planar shape, while in other embodiments the light transmissive
substrate 130 can include other geometries such as being convex or
concave in form such as for example being dome-shaped or cylindrical.

[0051] The wavelength conversion layer 140 may be deposited in direct
contact with the light transmissive substrate 130 without any intervening
layers or air gaps. The wavelength conversion layer may include one or
more photoluminescent materials distributed within a light transmissive
binder material. In one embodiment, one or more phosphor materials may be
thoroughly mixed in known proportions with a liquid light transmissive
binder material to form a suspension and the resulting phosphor
composition, "phosphor ink", deposited directly onto the light
transmissive substrate 130. The wavelength conversion layer 140 can be
deposited by screen printing, although other deposition techniques such
as slot die coating, spin coating or doctor blading can also be used. The
wavelength conversion layer 140 is then cured to form the daylight panel
100. In some embodiments, the wavelength conversion layer 140 can be a
planar shape, while in other embodiments the wavelength conversion layer
140 can include other geometries such as being convex or concave in form
such as for example being dome shaped or cylindrical.

[0052] The wavelength conversion layer 140 is configured to absorb at
least a proportion of the portion λ1 of the incident daylight
110 and convert it into light of different, longer wavelengths
λ4 (typically orange to red). Light of wavelengths
λ2 and λ3 that are not absorbed and converted by
the wavelength conversion layer 140 are transmitted through the
wavelength conversion layer 140 and contribute to the modified daylight
emission product 120. The modified daylight emission product 120 of the
daylight panel 100 is the combination of the unconverted wavelengths
λ1, wavelengths λ2 and λ3 of daylight
transmitted by the wavelength conversion layer 140 and the wavelengths
λ4 of light generated by the wavelength conversion layer 140.

[0053] The color spectrum of the modified daylight emission product 120
emitted by the daylight panel 100 depends on the phosphor material
composition and the quantity of phosphor material per unit area in the
wavelength conversion layer 140. Typically, the wavelength conversion
layer 140 can include a uniform distribution of the one or more phosphor
materials. In other embodiments, the wavelength conversion layer 140 may
include selective distribution or patterning of the one or more phosphor
materials. Selective distribution or patterning of the one or more
phosphor materials may allow for the daylight panel 100 to have clear
areas (i.e. devoid of phosphor materials) for viewing, whereas a uniform
distribution of the one or more phosphor materials may create a diffused
daylight panel 100 with no clear areas for viewing. The use of selective
distribution, patterning, or uniform distribution of phosphor materials
within the wavelength conversion layer 140 of the daylight panel 100 is
dependent on the particular application of the daylight panel 100. A
non-uniform distribution of one or more phosphor materials may also be
utilized, in which one or more phosphor materials are deposited in a
linear, nonlinear, or other distribution along the thickness of the
wavelength conversion layer 140.

[0054] The wavelength conversion layer 140 is preferably configured to
absorb at least a proportion of the portion λ1 of incident
daylight with wavelengths below about 480 nm and convert that portion
into light with a wavelength λ4 above about 590 nm. However,
it should be noted that the wavelength conversion layer 140 can be
configured to absorb various different portions of incident daylight for
converting into various different wavelengths. By configuring the
wavelength conversion layer 140 with different combinations and/or
distributions of the one or more phosphor materials, a modified daylight
emission product 120 can have a spectrum with a higher power density of
orange and red light and a lower power density of violet to blue light,
which is a "warm white" or "warmer white" color that is more preferable
for use in offices and homes. That is, the portions λ1,
λ2 of daylight may be selected to be different portions of the
daylight spectrum, and the portion λ1 of the daylight may be
converted to a different wavelength or set of wavelengths in order to
provide light with a different CCT.

Photoluminescent Materials

[0055] The one or more photoluminescent materials can comprise an
inorganic or organic phosphor and quantum dots that is capable of
generating light in the orange to red part of the spectrum. The inventors
have discovered that silicate-based yellow, silicate-based orange and
aluminum-silicate orange-red phosphors are preferred as they are readily
excitable by light of wavelengths 350 nm to 450 nm. Examples of possible
yellow silicate-based phosphors, orange silicate-based phosphors and
aluminum-silicate-based orange-red phosphors are given in TABLE 1. The
emission spectra for these phosphors is shown in FIG. 3A and the
excitation spectra for selected phosphors from TABLE 1 shown in FIG. 3B.
As can be seen from FIG. 3A whilst the phosphors are classified as yellow
and orange light emitting based on their peak emission wavelengths each
of the phosphors emits a significant portion of light in the orange and
red parts of the spectrum (i.e. at wavelengths of 600 nm and longer).

[0056] As disclosed in U.S. Pat. No. 7,311,858 B2 "Silicate-Based
Yellow-green Phosphors", the entire content of which is incorporated by
way of reference, the yellow silicate-based phosphors have a general
composition A2Si(O,D)4 in which Si is silicon, O is oxygen, A
includes at least one of strontium (Sr), calcium (Ca), barium (Ba),
magnesium (Mg), zinc (Zn) or cadmium (Cd) and D is a halogen fluorine
(F), chlorine (Cl), bromine (Br), iodine (I) or phosphorous (P), sulfur
(S) or nitrogen (N). Dopant D is present in the phosphor in an amount
ranging from about 0.01 to 20 mole percent and it is believed that at
least some of the dopant substitutes for oxygen anions to become
incorporated into the crystal lattice of the phosphor. More particularly
the yellow phosphor has the formula
(Sr1-x-BaxMy)2Si(O,D)4:Eu2+ where
0≦x≦1 and where 0≦y≦1 when M is Ca;
0≦y≦1 when M is Mg; and 0≦y≦1 when M is Zn
and Cd.

[0057] As disclosed in U.S. Pat. No. 7,655,156 B2 "Silicate-Based Orange
Phosphors", the entire content of which is incorporated by way of
reference, the orange silicate-based phosphors have a general composition
A3Si(O,D)5 in which Si is silicon, O is oxygen, A includes at
least one of strontium (Sr), barium (Ba), magnesium (Mg) or calcium (Ca)
and D is a halogen chlorine (Cl), fluorine (F) or nitrogen (N) or sulfur
(S). In one embodiment the silicate-based orange phosphor has the formula
(Sr1-xMx)yEuzSi05, where M is at least one of a
divalent metal Ba, Mg, Ca and/or Zn 0≦x≦0.5;
2.6≦y≦3.3; and 0.001≦z≦0.5 and subject to the
proviso that y is not 3 when M is Ba.

[0058] As disclosed in U.S. Pat. No. 7,648,650 B2 "Aluminum-Silicate Based
Orange-Red Phosphors with Mixed Divalent and Trivalent Cations", the
entire content of which is incorporated by way of reference, the
aluminum-silicate based orange phosphors have a general composition
(Sr1-x-yMxTy)3-mEum(Si1-zAlz)O5,
in which M is at least one of a divalent metal Ba, Mg, and/or Ca, T is a
trivalent metal Y, La, Ce, Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb,
Lu, Th, Pa or U; 0≦x≦0.4; 0≦y≦0.4;
0≦z≦0.2; and 0.001≦m≦0.5. Additionally such
phosphors can further include a halogen such as F, Cl or Br. It is
believed that such a halogen resides on oxygen lattice sites within the
silicate crystal.

[0059] It will be appreciated that the phosphor material is not limited to
the examples described and can include any suitable phosphor material,
including nitride and/or sulfate phosphor materials, oxy-nitrides and
oxy-sulfate phosphors or garnet materials (YAG).

[0060] In one embodiment a daylight panel for converting daylight to a
color temperature of 4000K, comprises a wavelength conversion layer 140
that includes a mixture of Orange 1 and Yellow 2 phosphors (TABLE 1). The
daylight color spectra, power density (Wm-2 nm-1) versus
wavelength (nm), for 4000K converted daylight and daylight are shown in
FIG. 4 for such a panel. The photopic response of the human eye is also
shown in FIG. 4. As can be seen in the figure, the modified daylight
spectrum includes a high power density (portion) of orange to red light
(e.g., wavelengths longer than about 600 nm) compared with the
unconverted daylight in a warm daylight product.

[0061] In another embodiment a daylight panel for converting daylight to a
color temperature of 3200K, comprises a wavelength conversion layer 140
that includes the Orange 1 phosphor (TABLE 1). The daylight color
spectra, power density (Wm-2 nm-1) versus wavelength (nm), for
3200K converted daylight and daylight are shown in FIG. 5 for such a
panel. The photopic response of the human eye is also shown in FIG. 5. As
can be seen in the figure, the modified daylight spectrum includes a high
power density (portion) of orange to red light (e.g., wavelengths longer
than about 600 nm) compared with the unconverted daylight resulting in a
warmer light product.

[0062] In other embodiments the wavelength conversion layer advantageously
includes the Orange 2 phosphor (TABLE 1). Such a phosphor is found to be
particularly suited for converting daylight to color temperatures of
2700K to 3500K. FIG. 6 is a portion of the CIE diagram showing daylight,
modified 3200K, 4000K and 4100K daylight and their relationship to the
black body curve. By appropriate selection of the phosphor material it is
possible to generate a converted daylight spectrum that lies within less
than three MacAdam ellipses of the black body curve.

[0063] While the wavelength conversion layer has been described as
comprising photoluminescent material in the form of phosphors, the
invention is applicable to any type of photoluminescent material, such as
quantum dots. For example, the photoluminescent material can comprise
quantum dots, such as for example, cadmium selenide (CdSe). The color of
light generated by a quantum dot is enabled by the quantum confinement
effect associated with the nano-crystal structure of the quantum dots.
The energy level of each quantum dot relates to the size of the quantum
dot. The larger quantum dots, such as red quantum dots, can absorb and
emit photons having a relatively lower energy (e.g. a relatively longer
wavelength). On the other hand, orange quantum dots which are smaller in
size can absorb and emit photons of a relatively higher energy (shorter
wavelength). Additionally, daylight panels are envisioned that use
cadmium free quantum dots and rare earth (RE) doped oxide colloidal
phosphor nano-particles, in order to avoid the toxicity of the cadmium in
the quantum dots.

[0065] The quantum dots material can comprise core/shell nano-crystals
containing different materials in an onion-like structure. For example,
the above described exemplary materials can be used as the core materials
for the core/shell nano-crystals.

[0066] The optical properties of the core nano-crystals in one material
can be altered by growing an epitaxial-type shell of another material.
Depending on the requirements, the core/shell nano-crystals can have a
single shell or multiple shells. The shell materials can be chosen based
on the band gap engineering. For example, the shell materials can have a
band gap larger than the core materials so that the shell of the
nano-crystals can separate the surface of the optically active core from
its surrounding medium.

[0067] In the case of the cadmium-based quantum dots, e.g., CdSe quantum
dots, the core/shell quantum dots can be synthesized using the formula of
CdSe/ZnS, CdSe/CdS, CdSe/ZnSe, CdSe/CdS/ZnS, or CdSe/ZnSe/ZnS. Similarly,
for CuInS2 quantum dots, the core/shell nano-crystals can be
synthesized using the formula of CuInS2/ZnS, CuInS2/CdS,
CuInS2/CuGaS2, CuInS2/CuGaS2/ZnS and so on.

[0068] Additionally, while FIG. 2 describes a daylight panel that includes
a wavelength conversion layer on a light transmissive substrate, other
embodiments of a daylight panel wherein photoluminescent material (e.g.,
phosphors or quantum dots) is distributed within a light transmissive
material can be utilized as well. In such embodiments, the
photoluminescent material may be selectively distributed, patterned,
uniformly distributed, and/or non-uniformly distributed within the light
transmissive substrate.

[0069] In addition to CCT, another property of light that may be improved
with the daylight panel 100 is the amount of lumens associated with the
emission product 120 of the daylight panel 100. Lumens are a measurement
of human eye sensitivity to a specific color. Blue, violet, and UV light
contribute a small amount of lumens to a light product because the eye is
less sensitive to shorter wavelengths, while orange and red light
contribute larger amounts of lumens to a light product because the eye is
more sensitive to these longer wavelengths. By converting shorter
wavelengths of daylight (e.g., blue, violet, UV) into longer wavelengths
(e.g., orange and red) using the daylight panel 100, more lumens can be
generated for the emission product 120 without sacrificing visible
portions of the blue spectrum.

[0070] FIG. 7A illustrates a daylight panel 100 in accordance with another
embodiment of the invention. The daylight panel 100 includes a light
transmissive substrate 130, a light diffusing layer 150, and a wavelength
conversion layer 140. The light transmissive substrate 130 and the
wavelength conversion layer 140 are the same as the light transmissive
substrate and the wavelength conversion layer described above with
respect to FIG. 2.

[0071] The light diffusing layer 150 includes a uniform thickness layer of
particles of a light reflective material, such as titanium dioxide
(TiO2). In alternative arrangements the light reflective material
can include barium sulfate (BaSO4), magnesium oxide (MgO), silicon
dioxide (SiO2), aluminum oxide (Al2O3) or a powdered
material with as high a reflectivity as possible, typically a reflectance
of 0.9 or higher. Any other suitable light reflective material may be
used if desired. The light reflective material powder is thoroughly mixed
in known proportions with a light transmissive binder material to form a
suspension. For aesthetic considerations, the light diffusive material is
typically white in color. In FIG. 7A, the resulting mixture is deposited
onto the face of the wavelength conversion layer 140. The diffusing layer
150 can be deposited by screen printing, although other deposition
techniques such as slot die coating, spin coating or doctor blading can
be used. The diffusing layer 150 is then cured to form the daylight panel
100.

[0072] The daylight panel 100 is configured such that the diffusing layer
150 is closest to the incident daylight 120, with the wavelength
conversion layer 140 being sandwiched between the diffusing layer 150 and
the light transmissive substrate 130.

[0073] The diffusing layer 150 improves the visual appearance of the
daylight panel 100 to an observer 160 looking at a surface of the
diffusing layer 150 (i.e. an observer on the outside of the panel)
because the light reflective material making up the diffusing layer 150
appears white to the observer. Moreover, the diffusing layer 150 also
reduces the effects of shadows associated with the angle of incident
daylight.

[0074] FIG. 7B illustrates a daylight panel 100 in accordance with another
embodiment of the invention. The daylight panel 100 operates
substantially the same as the daylight panel 100 of FIG. 7A. However, in
FIG. 7B the diffusing layer 150 is deposited onto the face of the light
transmissive substrate 130 rather than the wavelength conversion layer
140. The wavelength conversion layer 140 is then deposited onto the face
of the diffusing layer 150 in the same manner as described above to form
the daylight panel 100. Thus, the daylight panel 100 of FIG. 7B is
configured such that the light transmissive substrate 130 is closest to
the incident daylight 120, with the diffusing layer 150 being sandwiched
between the light transmissive substrate 130 and the wavelength
conversion layer 140.

[0075] In this embodiment the diffusing layer 150 improves the visual
appearance of the daylight panel 100 to an observer looking at a surface
of the light transmissive substrate because the light reflective material
making up the diffusing layer 150 appears white in color to an observer
160, which reduces the yellow appearance of the phosphor material (or
generally any colors from the phosphor material) within the wavelength
conversion layer. Moreover, the diffusing layer 150 of the daylight panel
100 in FIG. 7B also reduces the effects of shadows associated with the
angle of incident daylight 120.

[0076] FIG. 7C illustrates a daylight panel 100 in accordance with another
embodiment of the invention. The daylight panel 100 operates
substantially the same as the daylight panel of FIG. 7A. However, the
daylight panel 100 is configured such that the diffusing layer 150 is
closest to observer 160 on the underside of the daylight panel with the
wavelength conversion layer 140 being sandwiched between the light
transmissive substrate 130 and the diffusing layer 150.

[0077] The diffusing layer 150 improves the visual appearance of the
daylight panel 100 to an observer looking at a surface of the diffusing
layer because the light reflective material making up the diffusing layer
150 appears white to the observer 160.

[0078] Whilst FIGS. 7A-7C describe daylight panels 100 that include a
wavelength conversion layer 140, a diffusing layer 150, and a light
transmissive substrate 130, other embodiments may include a diffusing
layer situated on a layer of photoluminescent material (e.g., phosphors
or quantum dots) that is distributed within a light transmissive
material.

[0079] FIGS. 8A and 8B illustrate daylight panels in accordance with
alternative embodiments of the invention.

[0080] The daylight panel 100 of FIG. 8A is similar to the daylight panel
of FIG. 2, with the addition of another light transmissive substrate
130'. Additionally, the light transmissive substrates 130, 130' are
preferably, but need not be, hermetic. For hermetic substrates 130, 130',
the wavelength conversion layer 140 is located between the first light
transmissive hermetic substrate 130 and the second light transmissive
hermetic substrate 130'. The first light transmissive hermetic substrate
130 and the second light transmissive hermetic substrate 130'
respectively provide a barrier to a first surface of the wavelength
conversion layer 140 and a second surface of the wavelength conversion
layer 140. The surfaces of the wavelength conversion layer 140 may be in
direct contact with the light transmissive hermetic substrates 130, 130',
as depicted in FIG. 8A. The term "direct contact" for this embodiment
means that there are substantially no intervening layers or air gaps.
Creating direct contact at the interface between the wavelength
conversion layer 140 and either light transmissive hermetic substrate
130, 130' may be preferred to safeguard against non-ideal behavior of
light transmitting through the daylight panel 100. Furthermore, a light
transmissive hermetic substrate 130, 130' in direct contact with a
surface of the wavelength conversion layer 140 creates a barrier against
environmental contaminants, such as moisture that may affect the
performance of the phosphor.

[0081] The daylight panel 100 of FIG. 8B is similar to the daylight panels
of FIGS. 7A and 7B, with the addition of another light transmissive
substrate 130'. The light transmissive substrates 130, 130' are
preferably, but need not be hermetic. For hermetic substrates 130, 130',
the wavelength conversion layer 140 and diffusing layer 150 are located
between the first light transmissive hermetic substrate 130 and the
second light transmissive hermetic substrate 130'. The first light
transmissive hermetic substrate 130 and the second light transmissive
hermetic substrate 130' respectively provide a barrier to a first surface
of the wavelength conversion layer 140 and a first surface of the
diffusing layer 150. The surfaces of the wavelength conversion layer 140
and diffusing layer 150 may be in direct contact with the light
transmissive hermetic substrates 130, 130', as depicted in FIG. 8B. The
term "direct contact" in this context means that there are substantially
no intervening layers or air gaps. Creating direct contact at the
interface between the wavelength conversion layer 140 or diffusing layer
150 and either light transmissive hermetic substrate 130, 130' may be
preferred in order to safeguard against non-ideal behavior of light
transmitting through the daylight panel 100. Furthermore, a light
transmissive hermetic substrate 130, 130' in direct contact with a
surface of the wavelength conversion layer 140 or diffusing layer 150
creates a barrier against environmental contaminants.

[0082] FIG. 9A illustrates a light tube 200 in accordance with some
embodiments of the invention. The light tube 200 may be used in
conjunction with any of the daylight panels described above, e.g., with
respect to FIGS. 2, 7A-7C, 8A and 8B.

[0083] The light tube 200 is a tube or pipe that transports light from one
location to another. The light tube 200 may be implemented in a structure
210 (e.g., residential, commercial or industrial property) for
transporting daylight to an interior 220 of the structure and includes a
first surface 230 for receiving daylight 110 and a second surface 240 for
emitting modified daylight emission product 120 into the interior 220 of
the structure 210. In the embodiment illustrated in this figure, the
first surface 230 includes a daylight panel, such as those described
above with respect to FIGS. 2, 7A-7C, and 8A and 8B and the second
surface 240 comprises a light transmissive substrate (window). While the
first surface 230 is depicted in FIG. 9A as having a planar shape, it may
also have a dome shape to improve the light tube's 200 ability to receive
(capture) incident daylight 110. Daylight 110 incident on the first
surface 230 generates a modified daylight emission product 120 that
includes the combination of wavelengths λ1, λ2,
λ3 of daylight transmitted by the daylight panel 100 and the
wavelengths λ4 of light generated by the photoluminescent
material of the daylight panel 100 as described above with respect to
FIGS. 2, 7A-7C, 8A and 8B. The surface of the daylight panel facing the
daylight may be the light transmissive substrate 130, the wavelength
conversion layer 140, or the diffusing layer 150 depending on the
embodiment of the daylight panel used. The light tube 200 may be
substantially hollow, and/or may be filled in part with a waveguide
material.

[0084] The modified daylight emission product 120 is transported along the
light tube 200 through the second surface 240 (i.e. light transmissive
substrate) to illuminate the interior 220 of the structure 210. Typically
the inner surface of the light tube 200 is highly reflective to
facilitate the efficient transport of the modified daylight emission
product 120 from the first surface 230 to the second surface 230.
Additionally, the light tube 200 may be angled or flexible to facilitate
the transport of the emission product 120 from the first surface 230 to
the second surface 240. The light tube 200 may have any suitable shape
and may be fabricated form any suitable material. Moreover, the light
tube 200 may be implemented with a daylight panel that utilizes a uniform
distribution of the one or more phosphor materials or a selective
distribution or patterning of the one or more phosphor materials
depending on the application. The second surface 240 may be located at
one end of the light tube 200, as shown in FIG. 9A, or may be located at
any other suitable location along the length of the light tube 200. As
another example, the second surface 240 may be a volume that fills the
light tube 200, in whole or in part. Additionally, the second surface 240
may include a light diffusing layer to improve the visual appearance of
the second surface 240 to an observer facing the second surface 240.

[0085] FIG. 9B illustrates a light tube 200 in accordance with some other
embodiments of the invention. The light tube 200 may be used in
conjunction with any of the daylight panels 100 described above with
respect to FIGS. 2, 7A-7C, 8A and 8B.

[0086] As mentioned above, the light tube 200 is a tube or pipe that
transports light from one location to another and may be implemented in a
structure 210 (e.g., residential, commercial or industrial property) for
transporting daylight to the interior 220 of the structure. The light
tube 200 in FIG. 9B includes a first light receiving surface 230 and a
second light emitting surface 240, wherein the first surface 230
comprises a light transmissive substrate and the second surface 240
includes a daylight panel 100, such as those described above with respect
to FIGS. 2, 7A-7C, 8A and 8B. As illustrated in FIG. 9B, the first light
receiving surface 230 may have a dome shape to improve the light tube's
200 ability to receive (capture) incident daylight 110. Daylight 110
incident on the first surface 230 is transported along the light tube 200
to the second surface 240. At the second surface 240, the daylight panel
100 generates an emission product 120 that includes the combination of
wavelengths λ1, λ2, λ3 transmitted by
the daylight panel 100 and the wavelengths λ4 of light
generated by the photoluminescent material of the daylight panel 100 as
described above with respect to FIGS. 2, 7A-7C, and 8A-8B. The modified
daylight emission product 120 is used to illuminate the interior 210 of
the structure 220. Typically the inner surface of the light tube 200 is
highly reflective to ensure the efficient transport of daylight 110 from
the first surface 230 to the second surface 230. Additionally, the light
tube 200 may be angled or flexible. The light tube 200 may have any
suitable shape and may be fabricated from any suitable material.
Moreover, the light tube 200 may be implemented with a daylight panel
that utilizes a uniform distribution of the one or more phosphor
materials or a selective distribution or patterning of the one or more
phosphor materials depending on the application. In some embodiments, the
second surface 240 may include a diffusing layer to improve the visual
appearance of the surface to an observer as well as reduce the effect of
shadows from the angle of incident daylight. The light tube 200 may be
substantially hollow, and/or may be filled in part with a waveguide
material.

[0087] FIG. 9C illustrates a light tube 200 in accordance with some other
embodiments of the invention. The light tube 200 may be used in
conjunction with any of the daylight panels described above with respect
to FIGS. 2, 7A-7C, 8A and 8B.

[0088] As mentioned above, the light tube 200 is a tube or pipe that
transports light from one location to another and may be implemented in a
residential or commercial property 210 for transporting daylight to an
interior 220 of the residential/commercial environment. The light tube
200 includes a first surface 230 for receiving incident daylight, a
second surface 240 for emitting modified daylight 120 into the interior
of the structure 210 and a daylight panel 100, such as those described
above with respect to FIGS. 2, 7A-7C, 8A and 8B. While the first surface
230 in FIG. 9C is depicted as having a dome shape, it may alternatively
have a planar shape or other shape to optimize the light tube's 200
ability to capture incident daylight 110. In this embodiment the daylight
panel 100 is positioned within the light tube 200 between the first and
second surfaces 230, 240. Daylight 110 incident on the first surface 230
is transported along the light tube 200 to the daylight panel 100. At the
daylight panel 100, a modified daylight emission product 120 is generated
that includes the combination of wavelengths λ1,
λ2, λ3 transmitted by the daylight panel 100 and
the wavelengths λ4 of light generated by the photoluminescent
material within the daylight panel 100 as described above with respect to
FIGS. 2, 7A-7C, and 8A-8B. The modified daylight emission product 120 is
transported along the light tube 200 through the second surface 240,
where it is used to illuminate the interior 220 of the structure 210.
Typically the inner surface of the light tube 200 is highly reflective to
ensure the efficient transport of light from the first surface 230 to the
second surface 230. Additionally, the light tube 200 may be angled or
flexible and may be fabricated from any suitable material. Moreover, the
light tube 200 may be implemented with a daylight panel 100 that utilizes
a uniform distribution of the one or more phosphor materials or a
selective distribution or patterning of the one or more phosphor
materials depending on the application. The second surface 240 may be
located at one end of the light tube 200, as indicated in FIG. 9C, or may
be located at any other suitable location along the length of the light
tube 200. As another example, the second surface 240 may be a volume that
fills the light tube 200, in whole or in part. The light tube 200 may be
substantially hollow, and/or may be filled in part with an optical
medium.

[0089] By configuring the photoluminescent material of the daylight panel
with different combinations and distributions of the one or more phosphor
materials, a modified daylight emission product 120 can have a spectrum
with a higher power density of orange and red light and a lower power
density of violet to blue light (e.g., a more uniform color spectrum),
which results in a "warm white" or "warmer white" CCT that is more
preferable for use in offices and homes. Also, as mentioned above, by
converting shorter wavelengths of daylight (e.g., blue, violet, UV) into
longer wavelengths (e.g., orange and red) using the daylight panel, more
lumens can be generated for the emission product 120 without sacrificing
visible portions of the blue spectrum.

[0090] While the above embodiments of light tubes in FIGS. 9A, 9B, and 9C
describe the daylight panel as being implemented as a part of the first
surface, as a part of the second surface, or located between the first
and second surfaces, the daylight panel can comprise a part of the inner
light reflective surface of the light tube. In the latter it is
envisioned to provide the conversion layer directly to at least a part of
the inner surface of the light tube.

[0091] FIG. 10 illustrates a skylight 250 in accordance with some
embodiments of the invention. The skylight 250 may be implemented using
any of the daylight panels described above with respect to FIGS. 2,
7A-7C, 8A and 8B.

[0092] The skylight 250 is a light transmitting fenestration that forms
all, or a portion of, a roof or wall of a building or structure. The
skylight 250 may be implemented in a structure 210 (e.g., residential,
commercial or industrial property) for conveying daylight to the interior
220 of the structure 210. The skylight 250 may be implemented using any
of the daylight panels 100 described above with respect to FIGS. 2,
7A-7C, 8A and 8B. Daylight 110 (λ1, λ2,
λ3) incident on the skylight 250 is converted to generate a
modified daylight emission product 120 that includes the combination of
wavelengths λ1, λ2, λ3, transmitted by
the daylight panel 100 and the wavelengths λ4 of light
generated by the photoluminescent material within the daylight panel 100
as described above with respect to FIGS. 2, 7A-7C, 8A and 8B. The surface
of the daylight panel facing the daylight may be the light transmissive
substrate 130, the wavelength conversion layer 140, or the diffusing
layer 150 depending on the embodiment of the daylight panel used. The
modified daylight emission product 120 is used to illuminate the interior
220 of a residential/commercial structure 210.

[0093] While the skylight 250 in FIG. 10 is depicted as being flat
(planar), it is to be noted that the skylight 250 may be implemented in
various shapes, forms and sizes depending on its particular application.
For example, the skylight 250 may be dome-shaped or arcuate in form.
Additionally, the skylight 250 may be implemented with a daylight panel
that utilizes a uniform distribution of the one or more phosphor
materials or a selective distribution or patterning of the one or more
phosphor materials depending on the application.

[0094] By configuring the photoluminescent material of the daylight panel
100 that forms the skylight 250 with different combinations and
distributions of the one or more phosphor materials, an emission product
of the daylight panel can have a spectrum with a higher power density of
orange and red light and a lower power density of UV to blue light, which
results in a "warm white" or "warmer white" CCT that is can be more
preferable for use in offices and homes. Also, as mentioned above, by
converting shorter wavelengths of daylight (e.g., blue, violet, UV) into
longer wavelengths (e.g., orange and red) using the daylight panel, more
lumens can be generated for the emission product without sacrificing
visible portions of the blue spectrum.

[0095] FIG. 11 illustrates a window 260 in accordance with some
embodiments of the invention. A portion of the window 270 (upper in FIG.
11) may be implemented using any of the daylight panels described above
with respect to FIGS. 2, 7A-7C, 8A and 8B.

[0096] The window 260 is a transparent or translucent opening in a wall or
door that allows the passage of light. The window 260 may be implemented
in a structure (e.g., residential, commercial or industrial property) for
conveying daylight to the interior of the structure. Daylight 110
incident on the portion 270 of the window 260 implementing the daylight
panel 100 is converted into an modified daylight emission product as
described above with respect to FIGS. 2, 7A-7C, 8A and 8B, which is
combined with daylight transmitted through a portions 280 of the window
260 that do not implement the daylight panel to illuminate the
residential/commercial environment. The surface of the daylight panel 100
facing the daylight may be the light transmissive substrate, the
wavelength conversion layer, or the diffusing layer depending on the
embodiment of the daylight panel used. Furthermore, a diffusing layer may
be used on both sides of the portion 260 of the window 260 to improve the
visual appearance of the portion 260 of the window, as discussed above
with respect to FIGS. 7A-7C.

[0097] The window 260 may be implemented in various shapes in sizes
depending on its particular application. Additionally, the window 260 may
be implemented with a daylight panel that utilizes a uniform distribution
of the one or more phosphor materials or a selective distribution or
patterning of the one or more phosphor materials depending on the
application.

[0098] While the window 260 in FIG. 10 is depicted as implementing the
daylight panel in only a top portion 270, other configurations of the
window implementing the daylight panel may also be used. In some
embodiments, the entire window may be implemented using the daylight
panels described above with respect to FIGS. 2, 7A-7C, 8A and 8B. In
other embodiments, different combinations of different portions of the
window 260 may be implemented using the daylight panels described above
with respect to FIGS. 2, 7A-7C, 8A and 8B. In yet another embodiment, the
daylight panel may be implemented onto a shade for the window, e.g.,
where the shade is rolled up or down to change the amount of daylight
that is converted to phosphor light. In this embodiment, the material of
the shade provides a flexible substrate for the deposition of the
appropriate phosphor material(s).

[0099] By configuring the photoluminescent material of the daylight panel
that forms portions of the window with different combinations and
distributions of the one or more phosphor materials, an emission product
of the daylight panel can have a spectrum with a higher power density of
orange and red light and a lower power density of UV to blue light, which
results in a "warm white" or "warmer white" CCT. The "warm white" or
"warmer white" modified daylight emission product of the portions of the
window panel that implement the daylight panel are combined with daylight
transmitted through portions of the window panel that do not implement
the daylight panel to generate light with a CCT that can be more
preferable for use in offices and homes.

[0100] Also, as mentioned above, by converting shorter wavelengths of
daylight (e.g., blue, violet, UV) into longer wavelengths (e.g., orange
and red) using the daylight panel, more lumens can be generated for the
emission product without sacrificing visible portions of the blue
spectrum.

[0101] In the foregoing specification, the invention has been described
with reference to specific embodiments thereof. It will, however, be
evident that various modifications and changes may be made thereto
without departing from the broader spirit and scope of the invention. The
specification and drawings are, accordingly, to be regarded in an
illustrative rather than restrictive sense.